By incorporating a turbocharger into an engine of a vehicle, the efficiency and power output of the engine may be improved. Turbochargers may be adapted to a variety of engines types including conventional internal combustion, diesel, and hybrid engines, resulting in the increasing popularity of turbocharged vehicles. By forcibly inducting extra air into a combustion chamber of the engine, a proportional amount of additional fuel is ignited, producing more power than attained via air intake at ambient pressure. The pressurized, or boosted, air is typically heated during compression and if combusted directly, may increase the risk of engine knock. Thus, boosted air is often cooled by flowing the air through a charge-air cooler (CAC) before entering the engine intake manifold, a process that also increases the density of the air.
CACs, in order to effectively cool boosted air, are often large and bulky, resulting in production of vehicles with enlarged front ends compared to non-turbocharged automobiles to accommodate the size of the cooling system. As well, consumer demand has prioritized the development of more fuel-efficient, high performing vehicles which may be partially met by a CAC with smaller dimensions yet greater cooling capacity. Other attempts to address the improvement of current commercially available CACs include the use of water-cooled charge-air coolers (WCAC). One example approach is shown by Somhorst et al. in U.S. Patent Application No. 2017/0089253. Therein, a WCAC with an integrated multi-stage cooling is described that comprises two flow channels adapted to flow two coolants with different temperatures through the WCAC. The disclosed system provided a simpler, smaller device than previous examples of WCACs.
However, the inventors herein have recognized the above situation as well as potential issues with such systems. As one example, WCACs require an additional heat exchanger, driving up the overall cost of the cooling system. As well, WCACs are similarly limited in cooling capabilities as conventional air-to-air CACs and therefore may not experience improvement in performance while adhering to desired configurations.
In one example, the issues described above may be addressed by a method including during first conditions, cooling charge air from a compressor via air-to-air cooling and air-coolant conductive cooling at a hybrid charge air cooler (HCAC), during second conditions, cooling charge air from the compressor via the air-to-air cooling and via air-to-coolant convective cooling at the HCAC, and during third conditions, cooling charge air from the compressor via the air-to-air cooling and via chiller-assisted air-to-coolant convective cooling at the HCAC. In this way, both air-cooling and coolant-cooling may be utilized to exchange heat according to stages of boosted air heating during vehicle operation.
As one example, a HCAC may include an insert through which coolant may be circulated. The coolant may be stagnant during first conditions where heat extraction from the boosted air occurs by conduction to ram air flowing across a surface of the HCAC. During the second conditions, the coolant is allowed to circulate through the insert of the HCAC at ambient temperature, inducing heat transfer from the boosted air via convection in addition to the air-to-air heat exchange by conduction. Heat transfer by conduction and convection is continued through the third conditions but is assisted by additional cooling from a chiller arranged in the cooling circuit. Thus the heat transfer capacity of the HCAC is increased, allowing for a reduction in size of the HCAC unit compared to a conventional CAC without compromising efficiency or adding to manufacturing or operating costs.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.